The configuration illustrated, for example, in FIG. 10 of Japanese Published Patent Application No. 2002-90183, is an example of a conventional encoder signal processing circuit. FIG. 10 is a block view, abstracting the basic constituent parts for the purpose of counting the number of rotations of a rotary encoder.
FIG. 10 of Japanese Published Patent Application No. 2002-90183 is reproduced herein as FIG. 7. The encoder in FIG. 7 includes: a detection device 71, for detecting positional information from a code disc; a code disc 72, which includes the aforementioned positional information; a waveform shaping device 73, which shapes waveforms of positional data signals from the code disc that are detected by the aforementioned detection device; a data processing device 74, which processes positional data signals that are obtained from the waveform shaping device 73, and synchronize them to a predetermined clock; an edge detection device 75, which detects the rising (HP) and falling (LP) edges of data signals that are outputted from the data processing device 74; a selection device 76, which performs selection processing of rising signals (HP) and falling signals (LP) outputted from the edge detection device, and generates up count signals (UP) and down count signals (DOWN); a counting device 77, which counts up or count down, according to whether the aforementioned up count signals (UP) or down count signals (DOWN) are inputted; a timing generation device 78, which provides selection timing for the aforementioned detection device, and supplies a clock for the purpose of synchronization with data processing device 74 and edge detection device 75.
When the code disc of an encoder so arranged rotates, pulse signals, which are positional data signals corresponding to a slit in the code disc 72, according to the detection speed thereof, are emitted toward photosensors SA and SB, respectively. The waveform shaping device 73 removes noise, etc., from these pulse signals, and shapes them into generally rectangular shaped pulse waveforms DA1 and DB1, which can be inputted to a logic circuit.
These shaped positional data signals DA1 and DB1 are inputted to the data processing device 74, which operates to synchronize them with the slit detection timing signals. The data processing device 74 samples data signals according to a clock CK1, which is synchronized with the operation of detection device 71, which detects the slit, and maintains the input status of data signals DA1 and DB1, respectively.
DA2, one of the positional data signals that has been processed by the data processing device 74, is inputted to edge detection device 75. The edge detection device 75 detects the rising (HP) and falling (LP) edges of signals that are inputted, and output signals HP and LP, corresponding to these. The output of edge detection device 75 is inputted to the selection device 76. DB2, the other signal that is outputted from the data processing device 74, is inputted to the selection device 76, and the rotational direction of the encoder is determined from the output from the edge detection device 75. For each rotation, there is one pulse of UP output or DOWN output, corresponding to rotational direction CW (clockwise) or CCW (counterclockwise)
In the present example, there is a 90° phase difference between the phases of positional data signals DA1 and DA2, which are outputted according to rotational direction. The sequence of the positional data signals DA1 and DA2 can be ascertained based on the aforementioned rising (HP) and falling (LP) signals and rotational direction can be determined thereby.
Hence, the slit in the code disc 72 is detected on a predetermined cycle, according to the timing signal that is supplied by the timing generation device 78, as a positional detection signal, and this is changed into an UP or DOWN signal, depending on the phase relationship of the two signals. The number of rotations is counted by the counting device 77.
However, the waveform shaping device 73 requires a number of waveform shaping circuits corresponding to the detectors constituting the detection device 71, and if the number of detectors is increased, the number of waveform shaping circuits must also be increased. Reducing the number of parts is a response to the demand for miniaturization, but the presence of a multiplicity of waveform shaping circuits, duplicating similar functions, is believed to be a disadvantage. Reducing the number of circuits and other parts is also desirable from the standpoint of increased reliability and reduced energy consumption.